1. Field of the Invention
The present invention relates to a thermoplastic resin casing and a method for fabricating the same, and more particularly to a thermoplastic resin casing that has a three-dimensional structure having an outwardly protruding portion containing a curved surface, wherein a film having a decorative effect is laminated to a thermoplastic resin thereby providing a special decorative effect to the casing, and an edge portion of the thus laminated film is processed for fixing thereto, and a method for fabricating such a thermoplastic resin casing.
2. Description of the Related Art
Traditionally, a casing such as a container for holding an article therein or a case in which an electronic part is housed, or a casing such as a vehicle bumper, motorcycle cowl, helmet, or the like, has been fabricated in three dimensions by assembling plates made of metal or synthetic resin or like material, or has been molded as a one-piece, three-dimensional structure from a single plate. When coloring the exterior surface of the thus fabricated casing for decorative purposes, it is common to paint the surface of the casing or attach a colored sheet to it when the casing is made of metal. On the other hand, if the casing is made of a synthetic resin material, it is common to color the synthetic resin itself or to attach a colored sheet to it. Further, techniques such as plating, metal evaporation, etc. have been employed to provide metallic luster to the casing surface.
In the case of a casing made of a synthetic resin, the resin plate itself, which forms the casing, is colored to provide decorativeness to the casing. Alternatively, a colored sheet or a thin metallic film is attached or deposited as a decorative member over the surface of the resin plate that forms the casing.
In any of the resin casings fabricated by the prior art as described above, the decorative color applied to the casing surface is fixed and does not change at all or, if it does change, the change is limited. For example, in the case where a transparent colored sheet is laminated to the casing surface, the effect is such that the color of the colored sheet and the color of the casing itself seen through the transparent sheet are overlaid one on top of the other to present a mixture of two colors, but the appearance of the color does not change according to the way it is viewed.
As one method of providing such a special color effect, there is proposed a method that uses holography and creates image plane members to be applied to three-dimensional surfaces, thereby achieving a casing on which the shapes, colors, etc., of an image changes in various ways depending on the viewing angle. However, creating images to be reproduced, in particular, in white light by using the principle of holography requires a sophisticated technique and increases fabrication costs, and therefore, a method that uses holography is not a suitable method for fabricating inexpensive casings.
Apart from the method that uses holography, there is proposed a decoration method which, while employing a simple structure, can cause color patterns on a polyhedral body or a curved body to change in various ways depending on the viewing angle. In this decoration method, a casing having a polyhedral structure or a curved structure is formed from a transparent or translucent material, and the interior or exterior surface of the casing is covered with a plurality of polarizing film or plate pieces. In another proposed decoration method, a decorative thin film member, for example, a polarizing film, is bonded to one plane surface of an inorganic or resin substrate formed in a flat plate shape, to enhance richness in decoration and to add depth and three-dimensional effects to the texture.
In the above decoration method, a polarizing film or plate pieces are attached to the exterior or interior surface of the casing, which is a tedious and time-consuming process to decorate the casing, and it is not possible to cover the entire exterior or interior surface of the casing. As a result, if the pieces are attached to polygonal or curved surfaces of a casing, the decorative effect does not extend over the entire surface of the casing, and the effect is thus limited.
On the other hand, the polarizing film is bonded to the substrate to confer depth and three-dimensional effects to the texture. According to this decoration method, decorativeness can be easily provided as long as the substrate is formed in a flat plate shape. However, synthetic resin casings are often constructed in a variety of exterior shapes. As shown in the cross-sectional view of FIG. 1, when casing B is formed so as to have an outwardly protruding portion, and the entire casing is formed, for example, in a dish- or bowl-like shape, a curved surface is formed around the entire circumference of the exterior surface of the casing B.
When the exterior surface of the casing contains a curved surface, if the curved surface is uniaxial, a polarizing film can be bonded without creasing over the entire exterior surface. However, in the case of casing B shown in FIG. 1 in which a curved surface such as described by a three-dimensional curve is formed along the entire circumference of the protruding portion, it is difficult to bond a single polarizing film flatly along the curved surface without creasing over the entire surface of the protruding portion. If the polarizing film is to be bonded only to a flat surface portion of casing B, the polarizing film can be bonded without creasing, but if the flat surface portion has a protruding portion formed thereon, it is difficult to bond the polarizing film flatly without creasing over the surface of the protruding portion.
In view of the above, according to Japanese Unexamined Patent Publication No. H08-300399, there is proposed a decorative-film-coated molding fabrication method that can economically produce a molding coated with a decorative film having an excellent external appearance. In this decorative-film-coated molding fabrication method, first a preformed decorative film, which is cut to a size that extends beyond the edges of the molding to be coated with the film, is placed inside the mold, and then a molten resin is injected into the mold, allowing the edges of the decorative film to flow into the mold flash. Then, after the resin is cooled, and the molding is removed from the mold, the edges of the decorative film are trimmed off together with the mold flash, thus completing the fabrication of the molding coated with the decorative film.
However, in the decorative-film-coated molding fabrication method proposed above, since the preformed decorative film is placed inside the mold in which the resin is molded to produce the molding coated with the film, the decorative film must be sufficiently thick enough that it can retain its intended shape to a certain extent after preforming. Compared with this decorative film, the previously described polarizing film is thin and does not have a thickness suitable for such preforming, and therefore, the above fabrication method cannot be used in applications where a decorative effect is provided by attaching a polarizing film.
In view of the above, according to Japanese Unexamined Patent Publication No. H08-156016, there is proposed an in-mold decoration injection molding method by which a thin decorative film not suitable for preforming is applied to the surface of a resin molding simultaneously with the molding of the resin. The molding machine used in this in-mold decoration injection molding method comprises a cavity block and a core block disposed opposite each other in such a manner as to be closed and opened relative to each other, and a heating unit which is movable in a reciprocating fashion between an opposing space formed by the cavity block and core block and spaced apart from the opposing space.
In this molding machine, decorative film precut to a predetermined size is held onto the heating unit, and the heating unit is moved into the opposing space, and the decorative film while being heated by the heating unit contacts the mold surface of the cavity block by the application of vacuum. After retracting the heating unit from the opposing space, the cavity block and the core block are closed under pressure, and injection molding is performed, thereby laminating the decorative film to the surface of the molding. When the mold is opened, the heating unit is moved forward relative to the molding left on the core block, and the edges of the decorative film laminated to the molding are trimmed off to conform to the shape of the molding, thus removing excess film.
Further, according to Japanese Unexamined Patent Publication Nos. 2004-106598, 2005-119404, 2006-168267, etc., fabrication methods are proposed for moldings formed from foamed plastic substrates, wherein the decorative film and the foamed plastic substrate are bonded together during the molding of the foamed plastic substrate. In the molding fabrication method disclosed in Japanese Unexamined Patent Publication No. 2004-106598, when molding the foamed plastic substrate, the outer edge of the substrate is compressed flat, and the thus compressed flat portion is trimmed to make the cut end less visible from the outside, or the compressed flat portion is folded inwardly, thereby enhancing the appearance of the outer edge while increasing the rigidity of the structure.
In the molding fabrication method disclosed in Japanese Unexamined Patent Publication No. 2005-119404, a groove for hiding the cut end at the edge portion of the product is formed on the mold, and the appearance of the outer edge is enhanced by cutting the groove or by forming a product face substantially perpendicular to the vertical mold opening direction (operating direction) around the periphery of the product and then forming a folding portion extending from the product face into a flat shape. On the other hand, in the molding fabrication method disclosed in Japanese Unexamined Patent Publication No. 2006-168267, the excess edge of the foamed plastic substrate is cut off at the shear edge portion between the upper and lower molds for molding the product, and then the folding portion of the decorative film extending outwardly from the cut line is folded behind the foamed plastic substrate, thereby enhancing the appearance of the outer edge.
As described above, each of the molding fabrication methods for enhancing the appearance of the outer edge of the molding having a decorative film bonded thereto has concerned a the case in which the molding is formed from a foamed plastic substrate. However, in the case of a molding formed from a thermoplastic resin, these molding fabrication methods for enhancing the appearance of the outer edge of the molding cannot be directly used.
In view of the above, there is proposed a fabrication method for bonding a thin decorative film such as a polarizing film to a thermoplastic resin molding, wherein the decorative film and the thermoplastic resin plate are bonded together during the molding of the thermoplastic resin. In this fabrication method, first the decorative film is placed on a mold having a recess of a prescribed shape, and the recessed portion is evacuated to thermoform the decorative film into the prescribed shape; then, while retaining the film in that shape, an injection molding die having a shape that matches the recessed shape of the mold is placed onto the mold with the decorative film interposed therebetween, and the thermoplastic resin is injected through an injection hole formed in the injection molding die. After the injected thermoplastic resin has been formed into the prescribed shape in the recess of the mold, the injection molding die is withdrawn; in this way, the thermoplastic resin is formed into the prescribed shape only on the interior side of the decorative film in such a manner as to conform to the interior surface of the decorative film formed and retained in the prescribed shape. Then, any excess film is removed by trimming.
However, in the molding fabrication method proposed above, the molding formed from the thermoplastic resin is trimmed at its outer edge, while the decorative film cut at its outer edge is bonded to the thermoplastic resin, the endmost portion of the decorative film may partially delaminate and become jagged, depending on the handling of the molding or due to the chafing of the outer edge during use. As a result, while the decorative film can be bonded flatly without creasing over the surface of the molding, there arises a problem that the appearance of the molding as a whole degrades.
It is accordingly an object of the present invention to provide a thermoplastic resin casing that has a three-dimensional structure having an outwardly protruding portion containing a curved surface, wherein a film having a polarizing effect is laminated as a decorative film to a thermoplastic resin thereby providing a special decorative effect to the casing, and an edge portion of the laminated film is processed for fixing to an outer edge of the casing, and a method for fabricating such a thermoplastic resin casing.